From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 685DB6B0006 for ; Thu, 3 May 2018 17:04:05 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id z5so4428858pfz.6 for ; Thu, 03 May 2018 14:04:05 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id s1-v6si6424461plr.332.2018.05.03.14.04.04 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 03 May 2018 14:04:04 -0700 (PDT) Date: Thu, 3 May 2018 13:49:34 -0700 From: Davidlohr Bueso Subject: [PATCH 2/2] ipc/shm: fix shmat() nil address after round-down when remapping Message-ID: <20180503204934.kk63josdu6u53fbd@linux-n805> References: <20180503203243.15045-1-dave@stgolabs.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20180503203243.15045-1-dave@stgolabs.net> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org, aarcange@redhat.com Cc: joe.lawrence@redhat.com, gareth.evans@contextis.co.uk, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@kernel.org, dave@stgolabs.net shmat()'s SHM_REMAP option forbids passing a nil address for; this is in fact the very first thing we check for. Andrea reported that for SHM_RND|SHM_REMAP cases we can end up bypassing the initial addr check, but we need to check again if the address was rounded down to nil. As of this patch, such cases will return -EINVAL. Reported-by: Andrea Arcangeli Signed-off-by: Davidlohr Bueso --- ipc/shm.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/ipc/shm.c b/ipc/shm.c index b81d53c8f459..29978ee76c2e 100644 --- a/ipc/shm.c +++ b/ipc/shm.c @@ -1371,9 +1371,17 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, if (addr) { if (addr & (shmlba - 1)) { - if (shmflg & SHM_RND) + if (shmflg & SHM_RND) { addr &= ~(shmlba - 1); /* round down */ - else + + /* + * Ensure that the round-down is non-nil + * when remapping. This can happen for + * cases when addr < shmlba. + */ + if (!addr && (shmflg & SHM_REMAP)) + goto out; + } else #ifndef __ARCH_FORCE_SHMLBA if (addr & ~PAGE_MASK) #endif -- 2.13.6